Photonic crystal optical element having an active medium in a light confinement portion

ABSTRACT

The amount of outward shift of a lattice element (131a) and a lattice element (131b), the outward shift being symmetrical with respect to a resonator center on a straight line, is 0.42 to 0.5 times a lattice constant of a photonic crystal. The amount of outward shift of a lattice element (132a) and a lattice element (132b), the outward shift being symmetrical with respect to the resonator center on the straight line, is 0.26 to 0.38 times the lattice constant of the photonic crystal. The amount of outward shift of a lattice element (133a) and a lattice element (133b), the outward shift being symmetrical with respect to the resonator center on the straight line, is 0.13 to 0.19 times the lattice constant of the photonic crystal. The amount of outward shift of a lattice element (134a) and a lattice element (134b), the outward shift being symmetrical with respect to the resonator center on the straight line, is −0.1 to 0 times the lattice constant of the photonic crystal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a national phase entry of PCT Application No.PCT/JP2019/027115, filed on Jul. 9, 2019, which claims priority toJapanese Application No. 2018-131402, filed on Jul. 11, 2018, whichapplications are hereby incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a photonic crystal optical device thatis constituted by a two-dimensional slab-type photonic crystal.

BACKGROUND

In recent years, optical communication technology has becomeindispensable in order to deal with the increasing data volume ofcommunication and the Internet. In optical communication technology, itis necessary to multiplex, demultiplex, and process optical signalstransmitted by optical fibers for each line, and perform processing tosend the processed signals to the optical fibers again. Regardingoptical components that perform such processing, integrated on-chipoptical circuitry on a single chip is becoming more and more common.

In addition, data transmission in data centers and high-performancecomputers (HPCs) has been performed by means of optical fibercommunication, and a large number of compact and mass-produciblesurface-emitting lasers (VCSELs) have been employed as light sources. InVCSEL products, the footprint of a single laser is set to 10 μm or more,and the pitch of an array is set to 100 μm or more in order to achievesufficient performance in practical use.

Photonic crystals are becoming more and more important for furtherminiaturization and high integration of optical integrated circuits andfor the realization of nano-lasers that are even smaller and more powerefficient than VCSELs.

Photonic crystals are artificial materials that form a photonic bandstructure due to lattice elements with a cylindrical shape or the likeand a low refractive index being periodically arranged in a medium witha high refractive index, and realize control of light propagation. Inparticular, a photonic bandgap (PBG), in which a photonic crystal servesas light insulator, can be used to realize a nano-resonator thatconfines light to a small volume on a wavelength scale, and anano-waveguide that confines light to a width corresponding to severalcrystal holes.

Since a photonic crystal period is around 1/n (n: refractive index ofthe medium) of the optical wavelength in the vacuum, photonic crystalsare expected to reduce the size of optical integrated circuits by aroundone order of magnitude, and reduce power consumption by one order ofmagnitude or more, compared to the existing optical integrated circuits.Recently, current-injection room-temperature CW oscillation of aphotonic crystal laser has been realized (see Non-Patent Literature 1),and a 100-bit on-chip integrated optical memory has also been realized(see Non-Patent Literature 2). Thus, the performance of photonic crystaloptical components is becoming more and more practical.

A nano-resonator with a photonic crystal has a light confinement modethat is formed with a PBG that a surrounding photonic crystal has in adefective portion, which is formed by removing several crystal holes.The mode volume V in the light confinement mode is approximately1(λ_(c)/n)³ (λ_(c): resonant mode wavelength). Recent advances inresonator design have enabled the Q factor in the confinement mode to be10,000 or more, and it is characteristic that an extremely large Q/Vfactor that is difficult to achieve with anything other than photoniccrystals can be achieved.

An L-resonator is one of the aforementioned nano-resonators with aphotonic crystal. The L-resonator has a light confinement portion with alinear arrangement of point defects formed by removing lattice elementsof a two-dimensional slab-type photonic crystal. For example, an L1resonator is constituted by one point defect formed by removing alattice element from a lattice with lattice elements of a photoniccrystal. An L2 resonator is constituted by two point defects. An L3resonator is constituted by three point defects. In such L-resonators, aplurality of point defects are linearly arranged along a Γ-K crystalorientation.

The L3 resonators, of the nano-resonators, have attracted attentionbecause of the small size and a high Q factor thereof, and the use ofthe L3 resonators in laser devices to take advantage of a strongresonator enhancement effect has been considered from early. It has alsobeen reported that the L3 resonators are promising as optical memoriesthat enable high-capacity integration. In addition, the compact L1 andL2 resonators have not attracted much attention since a design thatincreases the Q factor had not been found until recently. Recently,however, a design of the L1 and L2 resonators that makes the Q factorsignificantly higher than that of the conventionally-designed L3resonators has been found. For example, it has been reported that, inorder to further enhance the Q factor of the L1-L3 resonators, the Qfactor in a resonator base mode is increased by shifting latticeelements on a main axis (on the extension of the main axis) on whichpoint defects are arranged, away from the resonator center at which thepoint defects are arranged (i.e. outward) (see Patent Literature 1 andNon-Patent Literature 3).

CITATION LIST Patent Literature

PTL 1 Japanese Patent No. 6317279

Non Patent Literature

NPL 1 S. Matsuo, T. Sato, K. Takeda, A. Shinya, K. Nozaki, H. Taniyama,M. Notomi, K. Hasebe, and T. Kakitsuka, “Ultralow Operating EnergyElectrically Driven Photonic Crystal Lasers”, IEEE Journal of SelectedTopics in Quantum Electronics, Vol. 19, No. 4, 4900311, 2013;

NPL 2 E. Kuramochi, K. Nozaki, A. Shinya, K. Takeda, T. Sato, S. Matsuo,H. Taniyama, H. Sumikura and M. Notomi, “Large-scale integration ofwavelength-addressable all-optical memories on a photonic crystal chip”,Nature Photonics, Vol. 8, pp. 474-481, 2014;

NPL 3 E. Kuramochi, E. Grossman, K. Nozaki, K. Takeda, A. Shinya, H.Taniyama, and M. Notomi, “Systematic hole-shifting of L-type nanocavitywith an ultrahigh Q factor”, Optics LETTERS, Vol. 39, No. 19, pp.5780-5783, 2014.

SUMMARY Technical Problem

A photonic crystal nano-resonator is an optical device of the smallestclass that confines light to a resonator with a micro-size that isapproximately equal to the wavelength of light, or several μm in termsof optical fiber communication wavelength. Meanwhile, an ordinarysemiconductor laser device has a much larger resonator size that issub-mm to several mm. As the study of nano-resonator lasers progresses,it has become apparent that there are problems specific to nano-lasersthat are not issues in ordinary semiconductor lasers.

For example, in the case of a laser device, the gain of the laser in aspecific resonant mode is brought about by an interaction between aresonant-mode electric field and an active layer. In the resonant mode,there are a large number of periodic nodes and antinodes correspondingto the wavelength (about the lattice constant of a photonic crystal) ina medium. However, in an ordinary semiconductor laser, there are a largenumber of antinodes in the active layer, and therefore, the relationshipbetween the position of each antinode and device characteristics isweak.

Meanwhile, for example, in a nano laser with a single quantum dot as anactive layer, whether or not the quantum dot is in a field antinodeportion is decisive for whether or not the laser oscillates.

In the case of an L-resonator with a small number of point defects, theresonant-mode electric field is concentrated on a few antinodes near thecenter, and thus, the positional relationship with the active layer isimportant. In the case of an L-resonator with odd-numbered point defects(L1, L3 etc.), one electric-field antinode is generated at the resonatorcenter in the base mode due to the symmetry of the photonic crystal.Since a small active layer, such as a quantum dot or a quantum wellembedded heterostructures (BH) used in Non-Patented Literatures 1 and 2,is arranged at the resonator center, it is convenient that the resonatorcenter is an antinode, for the sake of increasing the efficiency ofoptical devices such as lasers.

In contrast, in the case of an L-resonator with even-numbered pointdefects (L2, L4, etc.), the resonator center in the base mode is a nodeof the electric field due to the symmetry of the photonic crystal. Inthis case, the interaction between the base mode and the active layerweakens near the resonator center, and there is, therefore, concern anon-negligible decrease in device efficiency will be caused, especiallyin the L2 type whose resonator size is small.

Embodiments of the present invention have been made to solve theforegoing problems, and it is an object of embodiments of the presentinvention to enable an optical device such as a laser that uses an L2resonator, which is constituted by a two-dimensional slab-type photoniccrystal and performs active operation with an active layer, to operatein a first-order higher resonant mode.

Means for Solving the Problem

A photonic crystal optical device according to embodiments of thepresent invention includes: a photonic crystal body including: a baseportion; and a plurality of lattice elements with a columnar shape thatare periodically provided in a triangular lattice shape at intervals ofa wavelength of target light or less in the base portion, the pluralityof lattice elements having a refractive index different from that of thebase portion; a light confinement portion provided in the photoniccrystal body and formed with two point defects constituted by a portionin which no lattice element of a photonic crystal is present; an activemedium provided in the light confinement portion; and a first latticeelement pair, a second lattice element pair, a third lattice elementpair, and a fourth lattice element pair that are constituted by eightlattice elements continuously arranged on a straight line in a directionof a Γ-K crystal orientation of the photonic crystal on two sides of thelight confinement portion, with the light confinement portion at acenter, wherein an amount of outward shift of the first lattice elementpair that is a first pair from the center, the outward shift beingsymmetrical with respect to the center on the straight line, is 0.42 to0.5 times a lattice constant of the photonic crystal, an amount ofoutward shift of the second lattice element pair that is a second pairfrom the center, the outward shift being symmetrical with respect to thecenter on the straight line, is 0.26 to 0.38 times the lattice constantof the photonic crystal, an amount of outward shift of the third latticeelement pair that is a third pair from the center, the outward shiftbeing symmetrical with respect to the center on the straight line, is0.13 to 0.19 times the lattice constant of the photonic crystal, and anamount of outward shift of the fourth lattice element pair that is afourth pair from the center, the outward shift being symmetrical withrespect to the center on the straight line, is −0.1 to 0 times thelattice constant of the photonic crystal.

In the above-described photonic crystal optical device, the base portionis made of a semiconductor having a refractive index of 2 or more at anoperating wavelength.

In the above-described photonic crystal optical device, the activemedium is provided at a center of the light confinement portion.

In the above-described photonic crystal optical device, the activemedium is excited by means of current injection.

Effects of Embodiments of the Invention

As described above, according to embodiments of the present invention,the first lattice element pair, the second lattice element pair, thethird lattice element pair, and the fourth lattice element pair arrangedon two sides of the light confinement portion with this lightconfinement portion at the center are shifted by a predetermined amount.Thus, it is possible to obtain the excellent effect that an opticaldevice such as a laser that uses an L2 resonator, which is constitutedby a two-dimensional slab-type photonic crystal and performs activeoperation with an active layer is enabled to operate in a first-orderhigher resonant mode.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view showing a configuration of a photonic crystaloptical device in an embodiment of the present invention.

FIG. 2 is a distribution diagram showing distributions of electricfields in a first-order higher mode (a) and a zero-order base mode (b)of the photonic crystal optical device in the embodiment that areobtained by FDTD calculation.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Hereinafter, a photonic crystal optical device according to theembodiment of the present invention will be described with reference toFIG. 1. This photonic crystal optical device is constituted by a baseportion 102 and a photonic crystal body 101. Here, the photonic crystalbody 101 includes a plurality of lattice elements 103 with a columnarshape that are periodically provided in a triangular lattice atintervals of a wavelength of target light or less in the base portion102, the plurality of lattice elements 103 having a refractive indexdifferent from that of the base portion 102. The photonic crystal body101 is a so-called two-dimensional slab-type photonic crystal. Thelattice elements 103 have, for example, a cylindrical hollow structure.The base portion 102 is made of a semiconductor that has a refractiveindex value of 2 or more at an operating wavelength, such as indiumphosphorus or silicon.

In addition, this photonic crystal optical device includes a lightconfinement portion 104 that is provided in the photonic crystal body101, and is formed with two point defects provided in a portion in whichno lattice element 103 of the photonic crystal is present.

An active medium 105 is provided (embedded) in the light confinementportion 104. The active medium 105 is provided, for example, at thecenter of the light confinement portion 104. In this embodiment, theactive medium 105 has a BH structure with a size that fits into thelight confinement portion 104. For example, the active medium 105 has amultiple quantum well structure constituted by three quantum well layersthat are made of InGaAs and a barrier layer that is made of InGaAsP.Alternatively, the active medium 105 may be constituted by a single or aplurality of quantum dots, rather than quantum well layers. The activemedium 105 is not limited to the BH structure, and may alternatively bedistributed in the photonic crystal body 101 surrounding the lightconfinement portion 104.

An active optical device is constituted by a resonator that is formedwith the active medium 105 and the light confinement portion 104. Thephotonic crystal optical device in the embodiment is a laser. It hasbeen reported that laser oscillation occurs even in conventionally-knownphotonic crystal nano-resonators with a Q factor of 1,000 to 10,000, inthe case where the gain is generated in the active layer by means oflight excitation, or where pulse oscillation is also caused by means ofcurrent injection. On the other hand, as for the case of causingcontinuous oscillation at room temperature by means of DC currentinjection, there has been no report of oscillation except for photoniccrystal nano-resonators with a resonator-internal Q factor of more thantens of thousands, such as those described in Patent Literature 1 andNon-Patent Literatures 1 and 2. Therefore, embodiments of the presentinvention that increases the Q factor in the oscillation mode isparticularly important for current-injection oscillation laser devices.

The photonic crystal optical device according to embodiments of thepresent invention includes a first lattice element pair, a secondlattice element pair, a third lattice element pair, and a fourth latticeelement pair that are constituted by eight lattice elements, which arecontinuously arranged on a straight line in the direction of the Γ-Kcrystal orientation of the photonic crystal on two sides of theaforementioned light confinement portion 104, with this lightconfinement portion 104 at the center. Here, the first lattice elementpair is constituted by a lattice element 131 a and a lattice element 131b. The second lattice element pair is constituted by a lattice element132 a and a lattice element 132 b. The third lattice element pair isconstituted by a lattice element 133 a and a lattice element 133 b. Thefourth lattice element pair is constituted by a lattice element 134 aand a lattice element 134 b.

Note that the lattice element 131 a and the lattice element 131 b aresymmetrically arranged on a straight line in the direction of the Γ-Kcrystal orientation with the resonator center at the centertherebetween. The lattice element 132 a and the lattice element 132 bare symmetrically arranged on a straight line in the direction of theΓ-K crystal orientation with the resonator center at the centertherebetween. The lattice element 133 a and the lattice element 133 bare symmetrically arranged on a straight line in the direction of theΓ-K crystal orientation with the resonator center at the centertherebetween. The lattice element 134 a and the lattice element 134 bare symmetrically arranged on a straight line in the direction of theΓ-K crystal orientation with the resonator center at the centertherebetween.

The positions of the lattice elements 131 a, 131 b, 132 a, 132 b, 133 a,133 b, 134 a, and 134 b are shifted outward or inward, symmetricallyfrom the center on a straight line in the direction of the Γ-K crystalorientation. The shift direction is indicated by arrows in FIG. 1.

First, the amount of outward shift of the positions of the first latticeelement pair (lattice elements 131 a and 131 b), that is, the first pairfrom the resonator center is 0.42 to 0.5 times the lattice constant ofthe photonic crystal. Here, the shift is made on a straight line in thedirection of the -K crystal orientation and symmetrical with respect tothe resonator center.

Here, to make the Q factor in the first-order resonant mode high enoughto obtain laser oscillation, the shift amount of the positions of thefirst lattice element pair may be 0.40 a or more. Meanwhile, to suppressoscillation in the competing base mode, the Q factor in the base modeneeds to be sufficiently lower than that in the first-order higherresonant mode. For this purpose, the shift amount of the positions ofthe first lattice element pair needs to be 0.42 a or more. Also, if theshift amount of the positions of the first lattice element pair isgreater than 0.50 a, the performance begins to decline. Accordingly, theshift amount of the first lattice element pair is 0.42 a to 0.5 a.

The amount of outward shift of the positions of the second latticeelement pair (lattice elements 132 a and 132 b), that is, the secondpair from the resonator center is 0.26 to 0.38 times the latticeconstant of the photonic crystal. Here, the shift is made on theaforementioned straight line and symmetrical with respect to theresonator center.

The amount of outward shift of the positions of the third latticeelement pair (lattice elements 133 a and 133 b), that is, the third pairfrom the resonator center is 0.13 to 0.19 times the lattice constant ofthe photonic crystal. Here, the shift is made on the aforementionedstraight line and symmetrical with respect to the resonator center.

The amount of outward shift of the positions of the fourth latticeelement pair (lattice elements 134 a and 134 b), that is, the fourthpair from the resonator center is −0.1 to 0 times the lattice constantof the photonic crystal. Here, the shift is made on the aforementionedstraight line and symmetrical with respect to the resonator center. Inthis case, in other words, the amount of inward shift of the positionsof the fourth lattice element pair is 0 to 0.1 times the latticeconstant of the photonic crystal. Here, the shift is made on theaforementioned straight line and symmetrical with respect to theresonator center. To increase the Q factor in the first-order resonantmode, the best result is achieved when the shift amount of the fourthlattice element pair is −0.07 a, and the performance does not degrademuch with a shift amount of up to −0.1 a. However, the performancedegrades when the shift amount reaches −0.15 a.

By carrying out the mode of the photonic crystal optical deviceaccording to embodiments of the present invention such that each of theabove conditions is satisfied, the Q factor in the first-order highermode exceeds 10,000, and the Q factor in the base mode is suppressed toa lower level. As a result, continuous oscillation of the laser in thefirst-order higher mode can be obtained. Here, for example, excitationby means of injection of a current of around 10 μA into the activemedium 105 has been assumed.

Next, the results of the simulation will be described. Here, thefollowing conditions were assumed. It is assumed that the thickness ofthe base portion 102 that is made of silicon with a refractive index of3.46 is 250 nm, the lattice constant a is 420 nm, and the hole radius rof each lattice element is 101.5 nm. The active medium 105, which has amultiple quantum well structure, has a length of 950 nm in the directionof the resonator and a width of 300 nm. The thickness of a well layerthat constitutes the active medium 105 is 5 nm.

Electromagnetic field simulation in the resonator first-order highermode was conducted for this photonic crystal photonic device, using athree-dimensional FDTD method (See FIG. 2). The shift amount s1 of thefirst lattice element pair was 0.46a, the shift amount s2 of the secondlattice element pair was 0.34 a, the shift amount s3 of the thirdlattice element pair was 0.160 a, and the shift amount s4 of the fourthlattice element pair was −0.70 a. A Q factor of 81,000 was obtained at aresonator wavelength λ of 1503 nm in the first-order higher mode. In asample that was actually produced in the designing, continuousoscillation of the laser in the first-order higher mode was obtainedwith excitation by means of current injection into the active medium105.

As has been reported in Non-Patent Literature 3, an L-resonator has thebase mode and the first-order higher mode. Meanwhile, in theconventional technology, the use of the base mode and higher Q factorshave attracted attention, whereas an active use of the first-orderhigher mode has not been envisioned. Patent Literature 1 and Non-PatentLiterature 3 describe designs that maximize the Q factor in the basemode, and differ from embodiments of the present invention, whichmaximizes the Q factor in the first-order higher mode while suppressingthe Q factor in the base mode.

The base mode and the first-order higher mode of an L-resonator are inan inverse relationship with respect to whether the resonator center isa node or an antinode relative to the Γ-K crystal orientation along thelight confinement portion 104 and the lattice element pairs 131, 132,133, and 134. In the case of an L2 resonator, the electric field in thebase mode is an odd function and the resonator center is node, while theelectric field in the first-order higher mode is an even function andthe resonator center is an antinode. Therefore, the interaction betweenthe base mode and the active layer is suppressed near the center of theL2 resonator, and meanwhile, the interaction between the first-orderhigher mode and the active layer is enhanced.

If a laser is designed to oscillate in the base mode in a conventionalmanner, the emission efficiency is lost near the resonator center forthe above reasons. In addition, the Q factor in the first-order highermode is lower than that in the base mode, and thus, laser oscillationdoes not occur in the first-order higher mode. However, since thefirst-order higher mode strongly interacts with the active layer and hasa high radiation recombination efficiency, the injected currentpartially performs radiation recombination in the first-order highermode and is consumed, which further degrades the laser deviceefficiency.

According to embodiments of the present invention, when the first-orderhigher mode of an L2 resonator is used for laser oscillation, theinteraction with the active layer at the resonator center is strong asmentioned above, and thus, the laser device efficiency increases.Meanwhile, in the base mode, the interaction with the active layer atthe resonator center is weak, and thus, the consumption of injectedcurrent due to radiation recombination is suppressed. As a result, it ispossible to increase the laser device efficiency and optical output as awhole.

The characteristic of the L2 resonator that the first-order higher modestrongly interacts with the medium in the light confinement portion orthe active layer increases device performance of not only lasers andlight-emitting diode devices but also active optical devices such asoptical memories, optical receiver, and optical modulators. Thus,embodiments of the present invention are useful for these devices. Forexample, an active medium placed in a BH active layer may be any ofmaterials such as InGaAs, which can efficiently absorb signal light andconvert the absorbed signal light into electrical signals in the case ofoptical receivers, and quantum wells that include such InGaAs, as wellas materials such as InGaAsP that has a high optical nonlinearity inoptical devices such as optical modulators, optical switches, andoptical memories.

The characteristic that the resonator center of the L2 resonator is anode of a base-mode electric field and is an antinode of a first-orderhigher-mode electric field is also common in L4 and L6 resonators.Although the shift of the lattice element pairs of embodiments of thepresent invention is limited to the L2 resonator, the same effects canbe obtained with optical devices with L4 and L6 resonators if similarQ-factor control is realized. However, in such optical devices, thelight confinement is larger, and a plurality of electric field antinodesis included therein in both the base mode and the first-order highermode. For this reason, the effects of embodiments of the presentinvention are limited and obscure compared to the L2 resonator.

Note that the present invention is not limited to the embodimentdescribed above, and it is apparent that many variations andcombinations can be carried out by a person with an ordinary skill inthe art within the technical idea of the present invention.

REFERENCE SIGNS LIST

101 Photonic crystal body

102 Base portion

103 Lattice element

104 Light confinement portion

105 Active medium

131 a, 131 b, 132 a, 132 b, 133 a, 133 b, 134 a, 134 b Lattice element

The invention claimed is:
 1. A photonic crystal optical devicecomprising: a photonic crystal body including: a base portion; and aplurality of lattice elements with a columnar shape that areperiodically disposed in a triangular lattice at intervals of awavelength of target light or less in the base portion, the plurality oflattice elements having a refractive index different from that of thebase portion; a light confinement portion in the photonic crystal bodyand having two point defects provided by a portion of the photoniccrystal body in which none of the plurality of lattice elements arepresent; an active medium in the light confinement portion; and a firstlattice element pair, a second lattice element pair, a third latticeelement pair, and a fourth lattice element pair that are continuouslyarranged on a straight line in a direction of a Γ-K crystal orientationof the photonic crystal; wherein each of the first lattice element pair,the second lattice element pair, the third lattice element pair, and thefourth lattice element pair are disposed on opposing sides of the lightconfinement portion; wherein the light confinement portion is disposedat a center of the straight line; wherein an amount of outward shift ofthe first lattice element pair is symmetrical with respect to the centerof the straight line and is 0.42 to 0.5 times a lattice constant of thephotonic crystal; wherein an amount of outward shift of the secondlattice element pair is symmetrical with respect to the center on thestraight line and is 0.26 to 0.38 times the lattice constant of thephotonic crystal; wherein an amount of outward shift of the thirdlattice element pair is symmetrical with respect to the center on thestraight line and is 0.13 to 0.19 times the lattice constant of thephotonic crystal; wherein an amount of outward shift of the fourthlattice element pair is symmetrical with respect to the center on thestraight line and is −0.1 to 0 times the lattice constant of thephotonic crystal; and wherein the first lattice element pair, the secondlattice element pair, the third lattice element pair, and the fourthlattice element pair are arranged in this order from the center of thestraight line.
 2. The photonic crystal optical device according to claim1, wherein the base portion is made of a semiconductor having arefractive index of 2 or more at an operating wavelength.
 3. Thephotonic crystal optical device according to claim 1, wherein the activemedium is disposed at a center of the light confinement portion.
 4. Thephotonic crystal optical device according to claim 1, wherein the activemedium is configured to be excited by current injection.
 5. A photoniccrystal optical device comprising: a photonic crystal body including: abase portion; and a plurality of lattice elements with a columnar shapethat are periodically disposed in a triangular lattice at intervals of awavelength of target light or less in the base portion, the plurality oflattice elements having a refractive index different from that of thebase portion; a light confinement portion in the photonic crystal bodyand having two point defects provided by a portion of the photoniccrystal body in which none of the plurality of lattice elements arepresent; an active medium in the light confinement portion; and a firstlattice element pair arranged on a straight line in a direction of a Γ-Kcrystal orientation of the photonic crystal; wherein the first latticeelement pair is disposed on opposing sides of the light confinementportion; wherein the light confinement portion is disposed at a centerof the straight line; wherein an amount of outward shift of the firstlattice element pair is symmetrical with respect to the center of thestraight line and is 0.42 to 0.5 times a lattice constant of thephotonic crystal; and wherein the first lattice element pair is arrangedclosest to the light confinement portion among all lattice element pairson the straight line.
 6. The photonic crystal optical device of claim 5,further comprising a second lattice element pair arranged on thestraight line, wherein the second lattice element pair is disposed onopposing sides of the light confinement portion, and wherein an amountof outward shift of the second lattice element pair is symmetrical withrespect to the center on the straight line and is 0.26 to 0.38 times thelattice constant of the photonic crystal.
 7. The photonic crystaloptical device of claim 6, wherein the first lattice element pair isarranged between the second lattice element pair and center of thestraight line.
 8. The photonic crystal optical device of claim 6,further comprising a third lattice element pair arranged on the straightline, wherein the third lattice element pair is disposed on opposingsides of the light confinement portion, and wherein an amount of outwardshift of the third lattice element pair is symmetrical with respect tothe center on the straight line and is 0.13 to 0.19 times the latticeconstant of the photonic crystal.
 9. The photonic crystal optical deviceof claim 8, wherein the second lattice element pair is arranged betweenthe third lattice element pair and the first lattice element pair. 10.The photonic crystal optical device of claim 8, further comprising afourth lattice element pair arranged on the straight line, wherein thefourth lattice element pair is disposed on opposing sides of the lightconfinement portion, and wherein an amount of outward shift of thefourth lattice element pair is symmetrical with respect to the center onthe straight line and is −0.1 to 0 times the lattice constant of thephotonic crystal.
 11. The photonic crystal optical device of claim 10,wherein the third lattice element pair is arranged between the fourthlattice element pair and the second lattice element pair.
 12. Thephotonic crystal optical device according to claim 5, wherein the baseportion is made of a semiconductor having a refractive index of 2 ormore at an operating wavelength.
 13. The photonic crystal optical deviceaccording to claim 5, wherein the active medium is disposed at a centerof the light confinement portion.
 14. The photonic crystal opticaldevice according to claim 5, wherein the active medium is configured tobe excited by current injection.